Method for converting copper

ABSTRACT

A METHOD FOR REMOVING ANTIMONY FROM A MATERIAL WHICH COMPRISES AT LEAST ONE OF THE SUBSTANCES COPPER AND COPPER SULPHIDE. OXIDIZABLE IRON OR OXIDIZABLE IRON COMPOUNDS ARE ADDED TO THE MATERIAL WHILE THIS IS IN A MOLTEN CONDITION, THE SAID OXIDIZABLE IRON OR COMPOUND BEING OF A TYPE WHICH ARE SOLUBLE IN MOLTEN COPPER OR COPPER SULPHIDE AND WHICH HAVE A LOW ANTIMONY CONTENT. THE DISSOLVED IRON IS THEN ISOLATED FROM THE MELT BY A PARTIAL OXIDATION PROCESS, SIMULTANEOUSLY OXIDIZING ANTIMONY AND BINDING THE SAME TO THE IRON OXIDE.

United States Patent 3,744,992 METHGD FGR CONVERTING QOPPER Sven AndersLundquist, Skelleftehamn, Sweden, assignor to Boliden Ahtiebolag,Stockholm, Sweden No Drawing. Filed Nov. 39, 1970, Ser. No. 93,914Claims priority, application Sweden, Dec. 23, 1969, 17,828/69 Int. (ll.CZZb 15/14 US. Cl. 75-46 5 lClaims ABSTRACT OF THE DISCLOSURE A methodfor removing antimony from a material which comprises at least one ofthe substances copper and copper sulphide. Oxidizable iron or oxidizableiron compounds are added to the material while this is in a moltencondition, the said oxidizable iron or compound being of a type whichare soluble in molten copper or copper sulphide and which have a lowantimony content. The dissolved iron is then isolated from the melt by apartial oxidation process, simultaneously oxidizing antimony and bindingthe same to the iron oxide.

The present invention relates to a method for removing antimony from amaterial comprising at least one of the substances copper and coppersulphide.

In the manufacture of high grade copper, e.g. for use with electricalappliances, it is necessary to employ an electrolytic refining stage, inorder to obtain the requisite degree of purity of the copper. The anodesused in the electrolysis have a copper content of from 98.099.5% Cu and2.00.5% impurities, these impurities being substantially isolated duringthe actual process of electrolysis. The type and quantity of impuritiespresent in the copper to be electrolytically refined play an importantpart in the endeavour to obtain a trouble-free electrolysis. Strictlimits are placed on certain impurities, while greater tolerance ispermitted with regard to other impurities. It may therefore be necessaryto pre-refine the copper anode so that the permitted limits are notexceeded.

Antimony is a metal which has a particularly deleterious effect on thequality of copper refined by electrolysis and endeavours have been madeto reduce the quantity of antimony in such copper to a content of atmost 1 gram/ton. If the percentage of antimony in the copper anode istoo high, for example more than 350 gram/ ton, there is formed duringthe electrolysis a floating slime of antimony, arsenic and, in certaininstances, bismuth, which is liable to infect the copper cathode in amanner whereby the tolerance limits placed on the presence of antimonyin the electrolytically refined copper is exceeded, thereby jeopardizingthe quality of the copper. Moreover, this floating slime is also liableto result in growths on the cathode, which may cause short circuitingbetween the anode and the cathode, resulting in a reduced current yield.

Antimony can not generally be removed from antimony-containing copperminerals by enrichment processes, since in the majority ofantimony-containing copper finds the antimony is chemically bound to thecopper. Extensive separation of antimony by enrichment processe resultsin copper losses which are too high to make such processes economicallyfeasible. In order to reduce the content of antimony in copper products,it has hitherto been necessary to select crude materials of restrictedantimony content or to use various metallurgical processes which onlyafford limited antimony purification. A large number of ore finds, whichcan not be processed economically under present day conditions, would beac- Patented July 10, 1973 cessible for the production of high gradecopper if more effective antimony purification methods were to bedevised.

With currently used techniques, the copper is subjected to apre-refining process before being electrolytically refined, thepre-refining process including a number of metallurgical treatmentstages, such as roasting, matte smelting and conversion. Each stage ofthe refining process can be used to remove a certain percentage ofantimony. In the roasting stage, antimony is removed by volatilization,although expulsion of antimony seldom exceeds roughly 20% of the totalantimony content.

A slag builder, normally silicon dioxide, is charged to the processwhile smelting the roasted products, wherewith a slag and matte areformed which contain practically all the copper present in the chargedmaterial.

When smelting the roasted copper goods, generally called matte smelting,the antimony content is distributed between the slag and matte phases.It is not economically possible to influence this distribution to anygreat extent, for example by varying the composition or quantity of theslag.

Subsequent to separating the slag phase, the matte is transferred in amolten state to a converter, where it is oxidized with air or airenriched with oxygen-gas to form substantially copper metal, sulphurdioxide and iron oxides. The iron oxides are simultaneously converted toslag by adding silica sand.

The relatively long oxidation treatment in the converter is, in itself,an effective copper refining method, although it is far from suflicientwith respect to purifying the copper of antimony.

Several proposals have been made for reducing the antimony content inthe product obtained in the converter (the blister copper), includingtreatment methods using a solid or liquid slag. For example, it has beenproposed to use alkali (soda) as the main constituent in a refiningslag, whereby antimony oxides are more easily dissolved in the slag,thereby providing a slightly improved refining effect. Treatment withalkali is well known and generally employed. Treatment of blisteredcopper with CaO has also been proposed, as will be seen, for example,from the German Pat. No. 1,137,223. These refining methods have thedisadvantage that the effect afforded thereby is primarily dependent ondirect contact between the phase surfaces metal bath-slag bath and/ orsolid slag. Even though the metallurgical equilibrium according to theaforesaid German Patent indicates a good refining eifect, seriousdifliculties exist in practice in obtaining the requisite reactionvelocity.

These disadvantages are eliminated by means of the present invention,wherein the molten copper sulphide or the copper is added withoxidizable iron or oxidizable iron compounds which are soluble in moltencopper or copper sulphide and which have a low content of antimony,whereafter the dissolved iron is isolated in a conventional manner fromthe melt by partial oxidation with air or air enriched with oxygen-gas.Examples of suitable oxidizabie iron compounds are pyrites andpyrrhotite. These compounds are suitably charged to the process inpelletized form.

It has been established experimentally with respect to copper conversionthat the conversion of antimony from copper matte, copper sulphide orcopper metal to slag is directly correlated with the oxidation of ironin the matte and metal melt. When converting copper matte which containsantimony, the major portion of the antimony content passes from thecopper and is re-found in the converter slag. By studying the phases ofthe solidifying converter slag, inter alia in microprobes, it has beenestablished that antimony is present in an oxidized form and (Fe(I-I)Zn, Cu)0. (Fe(III), Al, Sb) O in which both copper and antimony arepresent in small concentrations.

The content of antimony of converter slags having different contents ofmagnetite was established experimentally and the results are shown inthe table given below:

Magnetite content: Antimony content This confirms the assumption thatthere is a strong chemical bond between iron and antimony in oxidizedform. By carefully following the copper conversion process, it wasclearly established that the antimony transfer rate from copper matteand copper metal to slag is functionally directly correlated with theoxidation of iron in the matte or copper.

Upon oxidation of the melt, the iron content is practically completelyoxidized before any appreciable quantity of copper is oxidized. Insulphurous environments, i.e. when the refinement process is to becarried out with matte melts, the sulphur from the sulphides is oxidizedin parallel with the iron and reduces the slag forming rate with aconstant supply of oxidant to the system. Subsequent to being oxidized,the iron oxide floats to the surface, bearing the isolated antimony. Theiron oxide is then either mechanically scraped from the surface of thecopper melt or, subsequent to forming slag with silicic acid, isdecanted 01f in liquid form.

The described refining method, in which iron or iron compounds having alow antimony content are charged to the refining system, is suitablycarried out in connection with copper conversion processes andin acopper converter, although, of course, it may be carried out in othertypes of furnaces, such as, for example, flame furnaces or rotaryfurnaces. Iron scrap, iron-copper-scrap, iron sulphides or chalcopyriteare examples of suitable iron additives free or essentially free fromantimony which can be charged to the system. The most efiective of thesewith respect to removing antimony is naturally iron scrap, while theleast effective is chalcopyrite, although when using iron scrap and ironsulphide the conversion period is lengthened without increasing theproduction of copper. Suitable oxidants are air-oxygen or air enrichedwith oxygen. The oxygen is preferably introduced beneath the surface ofthe bath, either by means of tuyeres or a lance.

The invention will now be illustrated with reference to the followingsingle example.

4 EXAMPLE In a copper converter which was charged with matte containing35% copper and 0.14% antimony, the copper sulphide, subsequent toblowing the matte, contained 0.04% antimony. For the purpose of furtherreducing the antimony content, granulated FeS was added in a quantity of6% of the quantity of copper and, subsequent to oxidation of thequantity of charged FeS to FeO and Fe O the antimony content in theready-blown copper had dropped to 0.02%. Other charges having the samestarting material and treated in the same manner, although lackingadditions of FeS, contained, subsequent to readyblowing, 0.035-0.040%Sb. With a later test, copper sulphide was treated in the same converterwith a matte of low copper content and low antimony content. The coppersulphide charge, approximately 130 tons, was treated with 10 tons ofmatte. The antimony content was reduced thereby from 0.06% to 0.03% inthe ready-blown copper. The antimony content, without the addition ofmatte of low copper content, was 0.045% after ready-blowing.

It is evident from the example that the method of the present inventionenables the antimony content in the produced copper to be considerablyreduced and that this reduction enables a material rich in antimony tobe processed without risk that the antimony content will impair thequality of the product.

What is claimed is:

1. A method for removing antimony from copper sulphide, characterized inthat to the copper sulphide in molten state is added oxidizable metalliciron which is soluble in molten copper sulphide and has a low content ofantimony, whereafter the dissolved iron is isolated from the melt by apartial oxidation, antimony being at the same time oxidized and bound tothe iron oxide, which forms a separate insoluble phase in the melt.

2. A method according to claim 1, characterized in that iron is added inthe form of scrap iron.

3. A method according to claim 1, characterized in that iron is added inthe form of iron-copper scrap.

4. A method according to claim 1, characterized in that the method iseffected in a copper converter.

5. A method according to claim 1, characterized in that oxidation iscarried out with oxygen-air or an air enriched with oxygen.

References Cited UNITED STATES PATENTS 103,434 5/ 1870 Du Motay --76970,686 9/ 1910 Clamer 7576 1,886,903 11/1932 Ralston et al. 75-743,258,330 6/1966 'Ito 7576 X 3,262,773 7/ 1966 Fritze 75.76 3,432,289 3/1969 Spitz 75-76 X 3,561,951 2/ 1971 Themelis 75-76 X L. DEWAYNERUTLEDGE, Primary Examiner J. E. LEGRU, Assistant Examiner

